a) Field of the Invention
The present invention relates to a set of lens systems which is to be used in various kinds of optical instruments such as cameras, video cameras, telescopes and microscopes.
b) Description of the Prior Art
Lens systems which are to be used in various kinds of optical instruments such as cameras, video cameras, telescopes, microscopes and endoscopes are ordinarily designed exclusively for the optical instruments in accordance with specifications of the instruments. Further, these lens systems generally have compositions consisting of large numbers of lens elements which are combined so as to improve optical performance of the instruments, and radii of curvature and glass materials have values which are designed exclusively for individual lens systems, whereby lens elements used for a lens system are rarely adopted for another lens system.
There are known examples wherein lens elements which compose optical systems are used commonly. One example is a camera or a microscope wherein a photographic lens system or an objective lens system is exchanged as a whole with another dependently on purposes of use. In this example, however, lens elements disposed in the lens systems are designed exclusively for the respective lens systems though the lens system as a whole is used commonly.
Another example which uses lens elements commonly is an attachment lens system for a front converter arranged before a lens system or a rear converter arranged after a lens system in a lens system of a camera or a video camrera and is used in a condition attached to different kinds of master lens systems. However, this attachment lens system is attached to the master lens systems mainly for changing axial focal lengths of the master lens systems but not for using lens elements themselves commonly.
Still another example which uses lens elements commonly is an optical experiment kit or the like which uses combinations of plural kinds of lens elements having different focal lengths which are prepared. However, these lens elements are combined simply to paraxially compose desired lens systems but not to obtain lens systems wherein aberrations are corrected sophisticatedly by combining the lens elements.
It has not been practiced to use lens elements themselves commonly to a plurality of lens elements in conventional optical systems as described above. The main reasons for the practical circumstances will be described below:
Aberrations of an ordinary lens element are remarkably varied by changing its radius of curvature, etc. since the lens element has extremely large freedom in its radius of curvature, thickness and glass material. In order to obtain desired optical performance by combining lens elements, it is therefore necessary to delicately define radii of curvature, thicknesses and glass materials of lens elements. In other words, a single lens element is extremely low in its versatility. Further, it is general that a single lens element has no sufficient capability to correct aberrations and can not be used independently in an optical instrument which requires optical performance of a high grade.
Conventional lens systems which do not allow lens elements to be used commonly to a plurality of lens systems constitute a high obstacle to reduce manufacturing costs of the lens systems.